Polyolefin-condensation polymer blend

ABSTRACT

A process for the preparation of a plastics blend which contains a polyolefin-condensation polymer blend, in the first step of which process a crystalline polyolefin component and a low-crystallinity polyolefin component are functionalized in one process step by grafting thereto a functional monomer and by pre-dispersing the polyolefins with each other, and in the second step the functionalized polyolefin component is mixed with a condensation polymer and, when so desired, with a non-functionalized olefin polymer, and with other components of the plastics blend.

The invention relates to a process for the preparation of a plasticsblend which contains a polyolefin--condensation polymer blend, by whichprocess a plastics blend having good thermomechanical pries is obtainedand-by which process the property profile of the plastics blend can beadjusted in a controlled manner. The invention also relates to the useof a plastics blend which contains a polyolefin--condensation polymerblend, produced by this process, in applications requiring differenttypes of processing methods, either as such or, for example as part of amultiple-layer product.

The use of plastics blends in the plastics industry is very common andvaried. Plastics blends are used mainly for two different reasons,namely, the use of blends is to a high degree dependent on cost factors,i.e. polymers having the desired properties but being expensive may bemixed at suitable proportions with more economical polymers. A secondfactor is that by a suitable combining of different polymers the goodproperties of each component are obtained in the product beingmanufactured. Plastics blends may, of course, contain in addition topolymers also fillers such as talcum, fiber reinforcements, etc.Furthermore, plastics blends may contain numerous additives of differenttypes, such as stabilizers, pigments, mold lubricants, foaming agents,fire retardants, etc. The most common methods of preparing plasticsblends are so-called melt-mixing methods or dry-mixing methods. Bymelt-mixing methods the different components can be combined, forexample, in an extruder within a suitable temperature range. Plasticsblends can be used, for example, in injection molding, fiber, film,thermoforming, extrusion, extrusion coating, lamination, and blowmolding applications.

Polyolefin--condensation polymer blends of various types are known inrather large numbers in the plastics industry. Condensationpolymerization is typically used for prepaing, for example, polyestersor polyamides. Blends of polyolefins and polyesters or polyamides arealso known in the patent literature.

EP patent publication 364 304 discloses a polyolefin-polyester blendwhich comprises 10-90% by weight a polyester in which the IV (intrinsicviscosity) is 0.30-1.20 and the quantity of carboxyl end groups is15-200 milliequivalents/kg, and 90-10% by weight a modified polyolefinhaving 0.2-5 mol. % epoxy or carboxylic groups and having a low meanmolar mass, i.e. 8000-14000. The blend is prepared first by dry mixingthe components and then by melt mixing them in, for example, a twinscrew extruder at. approx. 260° C.-320° C. The formed modifiedpolyolefin-polyester graft copolymer is used as a compatibilizer betweenpolycarbonates and polyolefins.

According to EP patent publication 443 736, the polyolefin-polyesterblend described above and prepared in a corresponding manner is, inturn, used as a compatibilizer between polyolefins and polyesters.

EP patent publication 336 320 discloses a complicated polymer blendwhich is made up of a carboxylic-acid(anhydride)-modified polypropylene,a saturated polyester, a copolymer containing epoxy groups, a modifiedor non-modified ethylene copolymer rubber, and an alkaline, preferablyamine-type, material.

Several plastics applications in which polyolefin-polyester/amide blendscan be used require that the plastic has good strength properties, suchas a good impact strength or elasticity modulus. However, there isusually the problem that, when one of the said properties is madesufficiently good, for example by means of a suitable mixing ratio or anelastomer addition, the other one is respectively deteriorated.Furthermore, the achieving of the desired properties has usuallyrequired higher contents of elastomeric polymer, which in turn resultsin a situation in which the property profile of the blend is no longercontrollable. Furthermore, problems may arise in the capacity of aplastics product containing such a polymer blend to be colored andpainted.

An object of the present invention has been to find, for the preparationof a plastics blend which contains a polyolefin--condensation polymerblend, a process by which it is possible to regulate the mechanical andthermomechanical properties of the blend prepared while the amounts ofthe basic components remains approximately unchanged.

It has also been an object of the invention to provide a plastics blendwhich contains a polyolefin--condensation polymer blend and has goodthermal resistance properties.

It has been a further object of the invention to find, for thepreparation of a plastics blend which contains apolyolefin--condensation polymer blend, a process by means of which thesynergistic properties of the components can be exploited optimally, forexample so that, when the impact strength of the product is increased,its elasticity modulus can be maintained at least at a sufficiently highlevel.

It is also an object of the invention to prepare a plastics blend whichcontains a polyolefin --condensation polymer blend in such a manner thata product made from such a blend can be easily painted or colored.

An object of the invention has also been to find a plastics blendpreparation process by means of which a minimal water absorption, a goodsurface quality and a high resistance to scratching and chemicals areachieved in a product.

It has been a further object of the invention to find a preparationprocess for a polyolefin --condensation polymer blend as a result ofwhich the preparation of the final plastics blend and the processibilityof the product are easier. Factors having a favorable effect onprocessibility include a low specific energy input (S.E.I.; kWh/kg),which correlates with easy miscibility, a wide processing temperaturerange, good melt flowability, good melt strength, and a short cycle time(in injection molding).

It has now been observed, surprisingly, that the good propertiesdescribed above can be obtained for a plastics blend which contains apolyolefin--condensation polymer blend by preparing the blend in twosteps; in the first step a controlled functionalization of thepolyolefins and their pre-dispersing with each other are performed, andin the second step they are mixed with a condensationpolymer/condensation polymers, and, when so desired, withnon-functionalized polyolefins, and with the other components of theplastics blend. The process according to the present invention ischaracterized in what is stated in the characterizing clause of claim 1.

The process according to the present invention can be used for preparingplastics blends in which the polyolefin--condensation polymer blend maycontain 5-95% by weight one or several condensation polymers, such as asaturated polyester or polyamide, and 95 -5% by weight olefin polymers,of which at least two contain functional groups. In addition, theplastics blend may contain inorganic fillers and fiber reinforcements,necessary additives, and possibly other polymers.

The olefin component of the polyolefin--condensation polymer blendcontained in the plastics blend prepared by the process according to theinvention is made up of crystalline olefin polymers and of olefinpolymers of low-crystallinity. Crystalline olefin polymer is defined inthis context as a polymer with a degree of crystallinity above 30%; thedegree of crystallinity of a polymer of low crystallinity isrespectively below 30%, in which case the polymer is elastomeric incharacter. Typical crystalline olefin polymers include the homopolymersof ethylene, propylene, 1-butene and 4-methyl-1 -pentene and copolymersin which the comonomer content is low, in general below 15%. Olefinpolymers of a low degree of crystalinity include the copolymers ofethylene with propylene, 1-butene, vinyl acetate and alkyl acrylates, aswell as ethylene-propylene(diene) elastomers.

According to the invention, the polyolefinic component of thepolyolefin--condensation polymer blend to be prepared is grafted withfunctional groups which can form interaction relationships with thecondensation polymers. These interaction relationships may be covalentin character, or they may be hydrogen or ion bonds with the condensationpolymer. Such functional groups producing interaction relationshipsinclude epoxy, hydroxy, anhydride, amine, amide, isocyanate, imide,silane and carboxylic groups, either as such or partially neutralizedwith (alkali) metal compounds.

Good and controllable mechanical and thermomechanical properties areobtained for the polyolefin--condensation polymer blend which contains apolyolefin component of the type described above, and thus for theactual plastics blend, by preparing the blend by the process accordingto the present invention. The essential idea in the process according tothe invention is thus that, in the first step of the two-step method, acontrolled functionalization of both crystaline and low-crystallinityolefin polymers and their pre-dispersing with each other are performed,and only thereafter is this polyolefin component mixed with the othercomponents.

The functionalization of the polyolefin component is carried out bygrating it with a functional monomer in molten state. Controlledfunctionlization of the polyolefin component means that both thecrystalline and the low-crystallinity olefin polymers are functionalizedin the same process step and apparatus. If the controlledfunctionalizing method according to the present invention were not used,it would in general result in that only the low-crystallinity olefinpolymer would become grafted, whereas the crystalline olefin wouldremain completely ungrafted or it would be grafted to an insufficientdegree, i.e. it would not be possible to control optimally the ratio ofthe functional monomer grafting of the crystalline olefin polymer tothat of the low-crystallinity olefin polymer.

According to a preferred embodiment, controlled functionalization of thepolyolefin component is achieved by feeding the crystalline olefinpolymer, the unsaturated functional monomer and the free radicalinitiator to the upstream end of an extruder, preferably a twin screwextruder.

The functional monomers may be carboxylic acids, carboxylic acidanhydrides or other carboxylic acid derivatives, such as esters,containing the above-mentioned functional groups. Imides as such orimidized from in-situ anhydride also belong to this group.

The free radical initiators are often peroxides, such as dialkylperoxides, dialkyl peroxides, peroxy acids, peroxy esters,hydroperoxides, and α-oxy- and α-peroxyhydroperoxides. Other freeradical initiators include azo-compounds, nitrosoanilides, andcombinations of dialkylperoxides with silanes.

In addition to a functional monomer it is also possible to use otherunsaturated monomers, such as aliphatic olefins, dienes, alkylacrylates, or aromatic vinyl monomers, by means of which the conversionof the functional monomer is promoted and the degradation of polyolefinssensitive to β-degradation is reduced.

The olefin polymer of low crystallinity is preferably fed in at a pointfurther downstream in the extruder, i.e. its feeding point in theextruder is at a distance of at least 5*D, typically 5* D-25*D from theupstream end of the extruder. D is the diameter of the extruder screw.This feeding order ensures that the free radical initiator fed in at theupstream end of the extruder has time at least in part to break downinto radicals and the functionalization of the crystalline polymer hashad time to start before the low-crystallinity olefin polymer is fedinto the extruder. Often it may additionally be preferable to feed inalso some free a at a point close to the feeding point of thelow-crystallinity olefin polymer. The extruder temperature is maintainedwithin a range of approx. 150° C.-300° C.

A polyolefin component functionalization implemented in the mannerdescribed above enables two different olefin polymers to befunctionalized and an advantageous morphology to be formed in acontrolled manner in one and the same process step, and thus thesynergic properties of the components to be exploited maximally in theend product. It is notable that the mechanical properties, above all theessential impact strength and rigidity, can be controlled with precisionby a change of the ratio between the functionalized polyolefin types(crystal/elastomeric). The preparation of the final plastics blend isalso easier, since the functional olefin polymers have beenpre-dispersed together already before the final melt mixing.

Furthermore, a piece made from a plastics blend which contains apolyolefin--condensation polymer blend prepared by the process accordingto the invention has a low water absorption, whereas, for example,polyamides normally absorb water to a detrimental degree; easycolorability and paintability are based on polarity achieved by means offunctionalization. Furthermore, it has been noted that the product has agood surface quality and a high resistance to scratching and chemicals.It is additionally highly preferable that good thermomechanicalproperties should be obtained for the end product even with low amountsof the functional olefin polymer; for example, even small contents ofelastomeric polyolefin, below 6% by weight, even 0.5% by weight, in thepolymer blend improve the impact strength of the product. Normally,elastomeric polymer contents of at minimum 10% by weight, and up to 30%by weight, are recommended. The process of the invention further makesit possible to use in the preparation of the final blend, in addition tothe functional polyolefin component, also non-functionalized olefinpolymers, a factor which, of course, has an advantageous effect also onthe price of the product.

According to the present invention, a functional olefin polymercomponent prepared in the manner described above and the othercomponents of the polymer blend, i.e. the condensation polymer andpossibly a non-functionalized olefin polymer, can be combined to form apolymer blend and further the final plastics blend, preferably in anextruder, more preferably a twin screw extruder. However, anymelt-mixing apparatus by means of which a sufficient mixing effect isachieved is suitable for the preparation of the final plastics blend.

The processibility of a plastics blend prepared by the process accordingto the invention has proved to be good. For example, it can be processedwithin a wide temperature range, it has good melt-strength andmelt-flowability properties, i.e. the molten plastics blend is an easilyhandled material, and a short cycle time considering, for example,injection molding applications.

The uses of a plastics blend prepared by the process according to theinvention, containing a polyolefin--condensation polymer blend, includeproducts requiring good impact strength and rigidity properties, forexample, in the automobile, packaging, sports equipment, electricalengineering and electronics industries.

The following figures, examples and tables illustrate in greater detailthe process for the preparation of a plastics blend which contains apolyolefin--condensation polymer blend and the properties of a productprocessed from the plastics blend prepared by this process, as well astheir comparison with the properties of a product processed from a blendprepared by a conventional process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a preferred feeding system for the functionalization ofolefin polymers (in a twin screw extruder).

In FIG. 1, reference numeral (1) indicates the first, i.e. principal,feeding zone, in which, in the process according to the invention, thefeeding in of the crystalline olefin polymer, the radical initiator, andthe functional unsaturated (+other unsaturated) monomer/s takes place.Reference numeral (2) indicates the second, i.e. force-feeding, zone, inwhich the feeding in of the low-crystallinity olefin polymer andpossibly the additional feeding in of a free-radical initiator takeplace. The distance between the feeding zones 1 and 2 is typically5*D-25*D, where D is the screw diameter.

EXAMPLE 1 (Reference Example)

Polypropylene (Neste Polypropylene VC12 12H, melt index MFR 12,manufacturer Neste Chemicals) was melt mixed with polybuteneterephthalate (Crastin S600, manufacturer Ciba-Geigy) and a chemicallymodified polypropylene (Exxelor PO X1 1015, manufacturer ExxonChemicals) in a Berstorff ZE25*33D twin screw extuder by using zonetemperatures of 240° C. and a screw velocity of 180 min⁻¹. The screwconfiguration used had three mixing elements. The feed proportions ofpolypropylene, polybutene terephtha-late and modified polypropylene were75%/20%/5%. Test bars were injection molded from the obtained polymerblend by means of a Krauss-Maffei KM 60-210B2 injection mold by usingzone temperatures of 230°-250 ° C. and a mold temperature of 65 ° C. Thethermomechanical properties of the test bars (Charpy notched impactstrength, tensile elasticity modulus, and HDT/B (heat distortiontemperature)) were measured according to ISO Standards ISO 179/1A, ISO/R527, and ISO 75. The results are shown in Table 1.

EXAMPLE 2 (Reference Example)

By the method described in Example 1, a polymer blend was prepared inwhich, instead of a chemically modified polypropylene, anethylene-butylacrylate-2,3-epoxypropyl-ter-polymer was used which had abutylacrylate content of 16% and a 2,3-epoxy-propylmetacrylate contentof 3% (experimental product, manufacturer Neste Chemicals). Thethermomechanical properties of the polymer blend obtained, Charpynotched impact strength, tensile elasticity modulus and HDT, weremeasured by using ISO Standards ISO 179/1A, ISO/R 527 and ISO 75. Theresults are shown in Table 1.

EXAMPLE 3

By the method described in Example 1, a polymer blend was prepared inwhich, instead of a chemically modified polypropylene, an olefin polymercomponent functionalized according to the present invention was used.This olefin polymer component was prepared in a Berstorff ZE 25*33D twinscrew extruder by feeding a crystalline homopolypropylene powder (meltindex 3.2, manufacturer Neste Chemicals), 2,3 -epoxypropylmetacrylate,and 1,3-bis(tertbutylperoxy-isopropyl)benzene (perkadox 14S, AkzoChimie) into the first feeding zone (1). A low-crystallinityethylene-butylacrylate copolymer having a butylacrylate content of 17%(Neste Polyethylene NCPE 6417, manufacturer Neste Chemicals) was fedinto the second feeding zone (2), 15*D further downstream in theextruder. The feeding conditions in the preparation of the functionalolefin components were:

polypropylene 67.9%,

ethylene-butylacrylate copolymer 29%,

2,3-epoxypropylmetacrylate 3%, and1,3-bis(tertbutylperoxy-isopropyl)benzene0.1%.

The extruder temperature profile used was 160°-180°-190°- . . . -190°C., and the rotation speed was 180 min¹. The final polymer blend wasprepared and injection molded into test bars in the manner described inExample 1. The results of the measurements of the thermomechanicalproperties in Table 1 demonstrate the excellent thermomechanicalproperties of the polymer blend prepared by the process according to theinvention as compared with the polymer blends according to the referenceexamples.

EXAMPLE 4

Popypropylene and ethylene-propylene-elastomer were functionalized bymeans of maleic acid anhydride by the process of the invention by usinga Berstorff ZE25*39.5D twin screw extruder. The screw velocity used was240 min⁻¹ and the temperature profile was 160°-180°-190°- . . . 190° C.The screw configuration used had two mixing zones: one before theforce-feeding point (2) and the other after the force-feeding point. Theforce-feeding point was located at a distance of 12*D from the principalfeeding point (1). The ethylene propylene-elastomer (EPR) (Keltan 740P,manufacturer DSM) was fed in at the force-feeding point. The othercomponents were fed in at the. principal feeding point. Thepolypropylene used was a PP-H powder, MFR 3.2, prepared by NesteChemicals, the maleic acid anhydride (MAH) was prepared by Chimie Linz,and the peroxide, Perkadox P14S, was prepared by Akzo Chimie. Twofunctionalized polyolefin blends were prepared, which had different EPRcontents:

4a: PP 89.45%+EPR 10% +MAH 0.5%+P14S 0.05%

4b: PP 59.45%+EPR 40%+MAH 0.5%+P14S 0.05%

The functionalized polyolefins 4a and 4b were further melt mixed with anon-functionalized polypropylene (VC12 33B, MFR 12, manufacturer NesteChemicals) and a polyamide-6 (PA6, Snia ASN/27/33/AV, manufacturer SniaTecnopolymeri) in the above-mentioned twin screw extruder by using ascrew velocity of 200 min⁻¹ and set temperatures of 240° C., at thefollowing mixing ratios:

4a1: 4a 5%+PP65%+PA6 30%

4a2: 4a 15%+PP 55%+PA6 30%

4b1: 4b 5%+PP 65%+PA6 30%

4b2: 4b 15%+PP 55%+PA6 30%

The thermomechanical properties of these blends, measured as in theprevious examples, are shown in Table 2.

The results show that the increasing of the elastomer proportion(compare blend 4a1 with 4b1, and blend 4a2 with 4b2) and the increasingof the functional component (compare blend 4a1 with 4a2 and blend 4b1with 4b2) improves the impact strength of the product significantly,while the tensile elasticity modulus decreases only slightly. It canalso be seen that, when the process according to the present inventionis used for preparing a polyolefin--condensation polymer blend, theimpact strength can be improved considerably even with low elastomercontents. The elastomer contents of the blends 4a1 . . . 4b2 are only0.5-6% by weight, whereas generally an elastomer addition of 10-30% isgenerally recommended for impact modification of polypropylene andpolyamide (cf. also the following Example 5).

EXAMPLE 5 (Reference Example)

Under conditions similar to those of blends 4a1 . . . 4b2 of Example 4,a blend was compounded which contained:

3% chemically modified polypropylene (Exxelor PO X1 1015), 30%ethylene-propylene-elastomer (Keltan 740P),

37% non-functionalized polypropylene (VC12 33B), and

30% polyamide (Snia ASN/27/33AV).

The Charpy notched impact strength, tensile elasticity modulus and HDT/Bwere measured from the products in a corresponding manner. The resultsare shown in Table 2.

                  TABLE 1                                                         ______________________________________                                        Thermomechanical properties of polymer blends                                              Reference                                                                              Reference                                                            example 1                                                                              example 2                                                                              Example 3                                      ______________________________________                                        Charpy notched impact                                                                        1,0        2,2      3,3                                        stregth (kJ/m.sup.2)                                                          Tensile elasticity modu-                                                                     1,6        1,4      1,6                                        lus (GPa)                                                                     HDT/B (°C.)                                                                           96         91       107                                        ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Thermomechanical properties of polymer blends                                             4a1   4a2     4b1     4b2   5                                     ______________________________________                                        Charpy notched impact                                                                       3,1     5,3     3,8   8,5   5,5                                 strength (kJ/m.sup.2)                                                         Tensile elasticity modulus                                                                  2,1     2,0     2,0   1,9   1,2                                 (GPa)                                                                         HDT/B (°C.)                                                                          122     118     123   113   106                                 ______________________________________                                    

We claim:
 1. A process for the preparation of a polyolefin-condensationpolymer blend, the polyolefin component of the blend being made up ofboth a crystalline polyolefin and a low-crystallinity polyolefin,wherein the polyolefin-condensation polymer blend is prepared in twosteps, of which the first step comprisesperforming a functionalizationof the polyolefin component, wherein said functionalization comprises(a)grafting the crystalline polyolefin with a functional monomer in amolten state; and (b) crafting the low-crystalline polyolefin with thefunctional monomer in a molten state, wherein the step of grafting thelow-crystalline polyolefin is performed after the commencement of thestep of grafting the crystalline polyolefin, and wherein the functionalmonomer contains at least one carbon-carbon double bond and a functionalepoxy, hydroxy, anhydride, amine, amide, isocyanate, imide, silane orcarboxylic group or corresponding metal complex, thereby forming apre-dispersion of functionalized polyolefins; and the second stepcomprises mixing the functionalized polyolefin component with thecondensation polymer component of the polymer blend or with thecondensation polymer component and a non-functionalized olefin polymer.2. A process according to claim 1, wherein the functionalization of thepolyolefin component is carried out in an extruder, in a processcomprisingfeeding the crystalline olefin polymer, an unsaturatedfunctional monomer, when so desired other unsaturated monomers, and afree-radical initiator into the upstream end of the extruder; andfeeding the low-crystallinity olefin polymer at a point furtherdownstream in the extruder at a distance of at minimum 5*D, where D isthe extruder screw diameter, from the upstream end of the extruder,wherein the temperature is within the range of 150° C.-300° C.
 3. Aprocess according to claim 2, wherein the extruder is a twin screwextruder.
 4. A process according to claim 2, wherein thelow-crystallinity olefin polymer is added at a distance of 5*D -25*Dfrom the upstream end of the extruder.
 5. A process according to claim1, wherein the second step of the process is carried out in anymelt-mixing apparatus having a sufficient mixing efficiency.
 6. Aprocess according to claim 5, wherein the melt-mixing apparatus is anextruder.
 7. A process according to claim 6, wherein the extruder is atwin screw extruder.
 8. A process according to claim 1, wherein thepolyolefin-condensation polymer blend contains 5-95% by weight of one ormore condensation polymers and 95-5% by weight an olefin polymer, atleast two of them containing functional groups.
 9. A process accordingto claim 1, wherein the condensation polymer is a polyester or apolyamide.
 10. A process according to claim 1, wherein thepolyolefin-condensation polymer blend further comprises fillers,reinforcements, necessary additives, and other polymers.
 11. A processaccording to any of the above claims, wherein the thermomechanicalproportions of the polyolefin-condensation polymer blend is adjusted bya changing of the proportions of the crystalline and thelow-crystallinity polyolefins in the polyolefin component.
 12. A processaccording to claim 1, wherein the monomer used in the functionalizationof the polyolefin component contains a functional anhydride group andthe condensation polymer is a polyamide.